[kccqzy]

That's not relevant at all. I think you have misunderstood the situation here. In Idris 1 the compiler and code generator is in Haskell, but the runtime is in C. So Scheme isn't exactly replacing Haskell but replacing C, for the runtime. (What replaced Haskell was Idris itself, by virtue of being self-hosting.)

The author even says that it's difficult to write C that deals well with the functional style of lots of little functions, and this is a problem Scheme also has and has solved. That's enough rationale to switch to Scheme:

> Generating good C code corresponding to a functional program which might have lots of small (and higher order) definitions is extremely challenging, so it is better to take advantage of someone else's work here.